Most complementary metal oxide semiconductor (CMOS) devices form a poly gate using polysilicon. When the poly gate is formed of polysilicon, a depletion layer is indispensably formed more or less. In the case where an integration degree of a device is not so large, a poly gate may be relatively large. Accordingly, even when the depletion layer is generated, reduction in electrical characteristics of a device may be ignored.
However, recently, as integrating technology for semiconductor devices has remarkably developed, the size of a gate gradually reduces and accordingly a depletion layer generated at the gate has a relatively large influence, which acts as a factor reducing the performance of a semiconductor device. The above-described matter emerges as a limitation of a semiconductor device using polysilicon.
To overcome this limitation, various technologies have been tried, and a metal gate has been proposed as a basic solution. However, the metal gate may have a difficulty in a manufacturing process, and forming a dual gate imposes relatively high costs.
For an alternative, a process of forming a fully silicided gate (e.g., using full silicide, or FUSI), is proposed as a transition to full metal gates. Metal silicides are generally considered to be metal-like materials.
However, a FUSI gate also has a difficulty in a process that when metal is deposited and a thermal diffusion process is performed after ions have been implanted in the polysilicon, a defect can be generated because thermal expansion coefficients of the deposited metal and polysilicon are different.